Try it yourself

Real popup, real Canvas page. Click the icon, then flip the switch.

Click the icon above → Watch the demo instead

canvas.instructure.com/courses/1738/grades

This embeds the real, unmodified extension popup (options.html) and a real captured Canvas grades page — the same DOM mutation the extension's content script performs is what toggles the grade on/off here.
Prefer to just watch? See the cinematic demo · Install the real extension